Method and apparatus for controlling a rotating biological contactor

ABSTRACT

A method and apparatus for controlling a rotating biological contactor. The weight of the biomass on the rotating members is monitored so that in the event that materials which are toxic to the biological slime is present in the waste water, the rate of weight loss from the rotating members can be determined and the flow of waste water to the rotating biological contactor can be controlled. To prevent back-up of the system, the waste water may be diverted to a diversion basin.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for controlling arotating biological contactor in which the rate of weight change ismonitored to determine the presence of conditions adverse to themaintenance of biological growth on the contactor.

2. Description of the Prior Art

In biochemical reactions, such as the treatment of waste water, it isknown in the art to measure changes in various conditions and to altertreatment of the reaction in response to such changes. Thus, forexample, in U.S. Pat. No. 3,684,202, activated sludge is recycled tomain sewage aerating tanks based on the measurement of the biologicaloxygen demand (BOD) of the sewage whereas in U.S. Pat. No. 4,130,481,the recycle is determined by sludge density and CO₂ production.

In U.S. Pat. No. 4,183,810, the BOD supply to a final denitrificationstep is controlled by analysis of the nitrite-plus-nitrate content inthe process liquid.

In U.S. Pat. No. 4,276,174, the temperature of an aerated mixture ofsludge is sensed and the rate of introducing oxygen-containing gas intothe mixture is controlled in response thereto.

In U.S. Pat. No. 4,277,342, sludge influent is treated in an aeratedmixing tank wherein the pH and the oxidation reduction potential ordissolved oxygen content is measured and acid and oxygen is respectivelysupplied in response to the measured levels.

In German Offenlegungsschrift No. 2532199, the activity ofmicroorganisms in a sewage treatment plant is supervised and controlledby the measured oxygen demand at the measured temperature, oxygenconcentration and turbidity level. In this system, pH values are keptconstant by the metered addition of acid or alkaline solution.

One means of treating waste water is through the use of rotatingbiological contactors wherein biological slimes on the contactorsaerobically digest the organic content in the waste water. Variousarrangements incorporating rotating biological contactors are describedin U.S. Pat. Nos. 3,484,836, 3,704,783 and 4,130,482. Additionally, U.S.Pat. No. 3,516,929, the inlet for the waste water flow to a plurality ofrotating contactors is opened or closed according to the liquid levelsensed by probes in the channel in which the contactors are located.

The use of rotating biological contactors provides an efficient andeffective manner of treating waste water. Unfortunately, it has beenfound that the biological slime on the contactors is sensitive to toxicmaterials whereby the presence of toxic materials in the waste water maydestroy the biological slime and render the rotating biologicalcontactors useless for their intended purpose. Conventional sensingdevices, such as those described previously, generally are not capableof determining an increase of those toxic materials which will adverselyaffect the biological slime. Moreover, even if sensing devices for thetoxic materials could be developed, the necessary level of sensitivitywould by difficult to achieve. In this regard, the constant contact withthe waste water would tend to corrode or foul the sensing device therebypreventing its operation or affecting its sensitivity.

OBJECTS AND SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea method and apparatus which overcomes or substantially alleviates theproblems of the prior art.

It is a more specific object of the present invention to provide amethod and apparatus for controlling a rotating biological contactor toreduce the effect of toxic materials on the biological slime on thecontactor.

Is is a further object of the present invention to provide a method andapparatus for controlling a rotating biological contactor in which thesensing means does not contact the waste water.

It is a still further object of the present invention to provide amethod and apparatus for controlling a rotating biological contactor inwhich the rate of weight change of the biological slime is measured and,in response to a relatively rapid decrease in weight, the waste waterflow to the contactor is controlled.

In accordance with one aspect, the present invention provides a methodfor controlling a rotating biological contactor which includes at leastone rotating member having a biomass of biological slime. The methodcomprises:

(a) passing waste water to the rotating biological contactor therebyestablishing a normal weight of the biomass on said at least onerotating member;

(b) monitoring the weight of the biomass on said at least one rotatingmember; and

(c) in response to a rate of weight loss greater than a predeterminedrate, controlling the passage of the waste water to the rotatingbiological contactor.

In accordance with another aspect, the present invention provides anapparatus for controlling a rotating biological contactor. The apparatuscomprises:

(a) a vessel having a liquid inlet for waste water and a liquid outlet;

(b) liquid flow control means connected to the liquid inlet;

(c) at least one rotating member having a biomass of biological slimethereon located in the vessel and connected to a rotating shaft;

(d) means for sensing the weight of the biomass; and

(e) controller means operably connected to the weight sensing means andthe liquid flow control means wherein upon the occurrence of a rate ofdecrease of the weight of the biomass greater than a predetermined rate,the flow of the waste water to the vessel is controlled.

Further advantages and features of the invention as well as the scope,nature and utilization of the invention, will become apparent to thoseskilled in the art from the following detailed description of thepreferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a rotating biological contactor and acontrol system in accordance with various aspects of the presentinvention. FIG. 2 is an end view of a rotating biological contactorshowing various suitable locations for the weight sensing means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As stated herein above, the present invention relates to a method andapparatus for controlling a rotating biological contactor. Rotatingbiological contactors, per se, are well known in the art as demonstratedby aforementioned U.S. Pat. Nos. 3,484,836, 3,516,929, 3,704,783 and4,130,482, the contents of which are incorporated by reference.

The rotating biological contactor is typically comprised of a vesselhaving a liquid inlet and a liquid outlet with at least one rotatingmember located in the vessel. The rotating member may be of any generalshape, but is usually a series of disks mounted on a shaft which extendstransverse to the direction of waste water flow from the liquid inlet tothe liquid outlet. The rotating members are coated with a biomass ofbiological slime such that they come into alternate contact with thewaste water to be treated and gaseous oxygen. The source of gaseousoxygen may be the ambient atmosphere or may be an oxygen-enrichedatmosphere in which case the rotating members would be located in anenclosed vessel.

The biological slime on the rotating members is principally composed ofaerobic bacteria which have the ability to adsorb, absorb, coagulate andoxidize various organic constituents in the waste water and to changesuch constituents into unobjectionable forms of matter. At the sametime, the biological slime increases the transfer of oxygen to the wastewater thereby promoting the multiplication or synthesis of the aerobicbacteria already present in the waste water and in the biological slimeon the rotating members, as well as increasing the ability of theaerobic bacteria to act upon the waste water and reduce it tounobjectionable forms.

Under normal operating conditions, the amount of the biological slime onthe rotating members approximates steady state. That is, as olderbacteria die, they are sloughed off the rotating members and arereplaced by new aerobic bacteria propagating under the aerobicconditions of the biological contactor. The effectiveness of therotating biological contactor depends solely on the ability of theaerobic bacteria to treat the organic contaminants in the waste waterand render them unobjectionable. Of course, the amount of bacteria onthe biological contactor will vary over a period of days depending onthe concentration of biodegradable material in the waste water.

Unfortunately, the aerobic bacteria are sensitive to the presence ofherbicides, pesticides and other types of toxic materials. Although theaerobic bacteria may be able to withstand a certain level of the toxicmaterial depending on the species of aerobic bacteria present in thebiological slime and the particular toxic material, beyond that levelthe aerobic bacteria will die and the rotating biological contactor willno longer be effective in treating waste water.

The present invention meets the stated problem by controlling the flowof the waste water to the rotating biological contactor whereby theaerobic bacteria in the biological slime is not unduly adverselyaffected. The invention may be appreciated by referring to anillustrative embodiment of the invention shown in FIG. 1. In thedrawing, waste water flows through line 10 and enters vessel 11containing rotating member 12. The waste water passing through line 10may be untreated or may be previously treated by gross filtration,comminution, floatation or other physical or chemical-physicalpretreatment processes. On the rotating member is a biomass ofbiological slime containing aerobic bacteria. The bacteria adsorbs,absorbs, coagulates and oxidizes the organic contaminants in the wastewater. Vessel 11 may be equipped with a lower outlet 13 for removingheavier materials accumulating at the bottom of the vessel or fordraining the vessel. The vessel may also be equipped with a cover (notshown) in the event that an oxygen-enriched atmosphere is to beemployed. Treated effluent leaves the vessel through line 14 and may besubsequently treated with a further rotating biological contactor and/orother conventional waste water treating steps (not shown).

Operably connected to the rotating member is a weight sensor 15 whichsends a signal indicative of the weight of the rotating member and thebiomass located thereon to controller 16. The weight sensor may be ofthe type known in the art which has been used for highway weighingstations and reaction vessels, hoppers, vats, blenders and tanks. Oneacceptable type of weight sensor is a load cell having a bonded straingage bridge and related circuit components enclosed in a hermeticallysealed housing which is available from Revere Corporation of America (adivision of Neptune Meter Company) located in Wallingford, Conn.

Controller 16 may be any known ana1og or digital computer which iscapable of receiving signals from weight sensor 15, calculating a rateof change of the weight of the rotating member, comparing the weight toa programmed, predetermined negative rate and, upon determining that thecalculated rate exceeds the programmed predetermined negative rate,transmits a signal. The signal is used to control valve 17 which willrestrict or terminate the flow of waste water through line 10.Controller 16 can also be selected so as to transmit a further signal tovalve 18 whereby the flow of waste water through line 10 is divertedthrough line 19 and into diversion basin 20. The signals may also beused to trigger an indicator, such as alarm 21, or otherwise signal thecondition of the apparatus.

As shown in FIG. 2 wherein the same reference numerals refer to theelements previously identified with respect to FIG. 1, vessel 11contains a plurality of rotating members, such as the one indicated byreference numeral 12, which are connected to rotating shaft 23. Whilethe drawing shows a single shaft with a plurality of rotating members,it is apparent that the vessel could contain a plurality of rotatingshaft with associated rotating members. In such an embodiment, theweight of the biomass on at least the rotating members closest to theinlet should be monitored since this biomass would presumedly be firstaffected by the presence of toxic materials in the waste water. Theshaft is driven by a variable speed motor 24 and is supported at theopposite end by bushing 25. At any of the points indicated by thetriangles, one or more weight sensors may be positioned. Morespecifically, the weight sensor may be located under the variable speedmotor, under the end bushing or under whatsoever bearings or bushingsare used to support the rotating shaft. Of course, the shaft should passthrough the sides of vessel 11 such that the measurement of the verticaldeflection of the shaft is not impaired. As illustrated in the figure,this may typically be achieved by supporting the weight sensors with afixed foundation. By locating the weight sensor at at least one of theselocations, the weight of the rotating member having the biomass thereoncan be measured by the weight sensor and a signal passed to controller16. This arrangement permits the condition of the biomass to be measuredaccurately without the necessity of a sensor contacting the waste water.

In operation, waste water passes through line 10 into vessel 11 whereinit is contacted with the biomass located on rotating members 12. Thedimensions of the vessel and the number and size of the rotating memberswill be determined based on the amount and degree of contamination ofthe waste water. However, a typical vessel may be from about 5 to about15 feet wide, from about 5 to about 30 feet long and from about 3 toabout 10 feet deep. The vessel typically contains from about 5 to about400 rotating members of disk-like shape each being from about 5 to about15 feet in diameter with the rotational rate of the rotating membersvarying from about 1 to about 5 rpm. An illustrative arrangement is avessel having a width of 14 feet, a length of 26 feet and a depth of 7feet with one shaft rotating at 1.5 rpm and having 400 rotating memberseach 12 feet in diameter. Thus, in this arrangement, the edges of eachrotating member has about a one foot clearance to the sides of thevessel.

The organic contaminants in the waste water are adsorbed, absorbed,coagulated and oxidized into unobjectionable forms of matter and thetreated effluent passes from the vessel via line 14 for recovery orfurther treatment. Sludge accumulating in the vessel may be removed byopening the valve in line 13.

The weight of the rotating member including the biological slime ismeasured by weight sensor 15 and a signal is transmitted to controller16. By measuring the weight of the rotating member or members when thereis no biological slime thereon and further measuring the member ormembers when the contactor is operating normally, the total quantity ofthe biomass may be determined. In the event that measurements from theweight sensor indicate that from about 5 to about 50 percent, preferablyfrom about 10 to about 20 percent by weight of the biomass has beensloughed off the rotating members within from about 1 to about 100minutes, preferably from about 5 to about 20 minutes, the controllerreacts by restricting or terminating flow through valve 17. The preciseweight loss and time period for a particular biological contactor isdetermined according to such factors as the flow rate of the wastewater, the quantity of biodegradable matter in the waste water and thetype of toxic wastes expected to be encountered.

In addition to controlling the flow to the contactor, the controller 16may also open valve 18 whereby wastewater is diverted through line 19into diversion basement 20. Additionally, the controller may signal theoperator by indicating the weight loss and by showing the positions ofvalves 17 and 18.

Modifications of the above-described embodiments of the invention thatare obvious to those of ordinary skill in the waste water art or relatedart are intended to be within the scope of the following claims.

What is claimed is:
 1. A method of controlling a rotating biologicalcontactor which includes at least one rotating member having a biomassof biological slime, said method comprising:(a) passing waste water tothe rotating biological contactor thereby establishing a normal weightof the biomass on said at least one rotating member; (b) monitoring theweight of the biomass on said at least one rotating member; and (c) inresponse to a rate of weight loss greater than a predetermined rate,controlling the passage of the waste water to the rotating biologicalcontactor.
 2. The method of claim 1 wherein the predetermined rate ofweight loss is in the range of from about 5 to about 50 percent byweight of the biomass over from about 1 to about 100 minutes.
 3. Themethod of claim 1 wherein the rotating biological contactor includes aplurality of rotating members located on a common rotating shaft.
 4. Themethod of claim 3 wherein the weight of the biomass is monitored bymonitoring the weight of the shaft.
 5. The method of claim 1 wherein thepassage of waste water to the rotating biological contactor iscontrolled by terminating the flow of waste water to the contactor. 6.The method of claim 5 wherein the passage of the waste water is furthercontrolled by diverting the waste water to a diversion basin.
 7. Themethod of claim 1 wherein the predetermined rate of weight loss is inthe range of from about 10 to about 20 percent by weight of the biomassover from about 5 to about 20 minutes.
 8. An apparatus for controlling arotating biological contactor comprising:(a) a vessel having a liquidinlet for waste water and a liquid outlet; (b) liquid flow control meansconnected to the liquid inlet; (c) at least one rotating member having abiomass of biological slime thereon located in the vessel and connectedto a rotating shaft; (d) means for sensing the weight of the biomass;and (e) controller means operably connected to the weight sensing meansand the liquid flow control means wherein upon the occurrence of a rateof decrease of the weight of the biomass greater than a predeterminedrate, the flow of the waste water to the vessel is controlled.
 9. Theapparatus of claim 8 wherein the rotating biological contactor includesa plurality of rotating members on the rotating shaft.
 10. The apparatusof claim 9 wherein the weight sensing means senses the weight of therotating shaft.
 11. The apparatus of claim 9 wherein the rotating shaftis driven by a variable speed motor and the weight sensing means sensesthe weight of the motor.
 12. The apparatus of claim 9 wherein therotating shaft has a bushing at one end and the weight sensing meanssenses the weight of the bushing.
 13. The apparatus of claim 8 whereinthe controller means is further operably connected to a second liquidcontrol means whereby waste water may be diverted from the vessel to adiversion basin.
 14. The apparatus of claim 8 wherein the controllermeans is connected to an indicator means.
 15. The apparatus of claim 8wherein the controller means is connected to an alarm.
 16. The apparatusof claim 8 wherein the vessel contains a plurality of rotating memberson a plurality of rotating shafts.
 17. The apparatus of claim 8 whereinthe controller means controls the flow of waste water to the vessel whenthe sensing means senses a weight loss of from about 5 to about 50percent by weight over from about 1 to about 100 minutes.
 18. Theapparatus of claim 8 wherein the controller means controls the flow ofwaste water to the vessel when the sensing means senses a weight loss offrom about 10 to about 20 percent by weight over from about 5 to about20 minutes.